The present invention relates to a control device for an at least partially four-wheel-driven motor vehicle. More particularly, the present invention relates to a control device for an at least partially four-wheel-driven motor vehicle, having a control unit which variably distributes a driving torque of a drive unit to primary driving wheels, which are permanently connected with the drive unit, and to secondary driving wheels which, if required, can be connected by way of a transfer clutch with the drive unit, wherein the control unit determines a desired clutch torque which is to be set by an actuator device at the transfer clutch.
A control device of this type is described, for example, in German Patent Document DE 100 54 023 A1. Accordingly, a torque distribution device is known for changing the torque distribution ratio between the wheels of the front axle and the wheels of the rear axle by a corresponding control of a friction clutch as a longitudinal blocking device (e.g., transfer clutch). The driving action of a vehicle can be influenced considerably by the determination of a torque distribution ratio. In particular, the object of German Patent Document DE 100 54 023 A1 relates to the driving dynamics when cornering. In this case, a partially four-wheel-driven motor vehicle may be a basically front-wheel-driven motor vehicle with a rear-wheel drive which can be connected by means of a transfer clutch; a basically rear-wheel-driven motor vehicle with a front-wheel drive which can be connected by way of a transfer clutch; or a permanent all-wheel drive vehicle with a controllable transfer clutch for changing the torque distribution between the front and rear axle.
In general, as discussed below, primary driving wheels are the wheels which are permanently connected with the drive unit, and secondary driving wheels are the wheels which, if required, can be connected with the drive unit by way of the transfer clutch.
Furthermore, such known control systems usually have a control of the transfer clutch as a function of the rotational speed difference between a rotational speed of the primary driving axle and the rotational speed of the secondary driving axle (for example, German Patent Document DE 34 27725 C2).
It is an object of the present invention to improve a control system of the previously mentioned type with respect to the precision of the control.
The present invention is based on the recognition that, in the case of an all-wheel drive torque distribution, the driver's intention is important and usually relates to high or considerably changing power demands while the traction is optimal. For this reason, particularly the accelerator pedal position and also the change of the accelerator pedal position may be taken into account. Simultaneously, but to a lesser degree, the limits of the traction optimization may also be taken into account. These are defined by driving situations or vehicle conditions by which a twisting of the transmission line is caused. In this case, it may be taken into account that twisting occurs, particularly when cornering or when maneuvering into or out of parking spaces (depending on the steering angle), but also in the case of large rotational wheel speed differences (depending on blind torques) (for example, as a result of different tire circumferences). It is also important in the case of the control device according to the invention that the long-term component protection with respect to mechanical wear and temperature-caused stress are taken into account (depending on the vehicle speed and the driving torque). Finally, in addition, comfort is also increased, particularly when starting (depending on the rotational engine speed).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.